The present invention relates generally to the field of work vehicles. It relates more particularly to removal of braking heat from an axle of a wheeled loader.
Some work vehicles, such as end loaders, must change their directions of movement frequently. To do this, wheel or live axle brakes are generally used to first bring the vehicle to a stop. When this is done frequently, the brakes become overheated.
This has sometimes been resolved by placing the brakes inside an axle housing, where the heat generated by brake friction is removed from the brake by an axle lubricating bath. The lubricant spreads the heat over the entire interior surface of the axle housing, whereupon thermal conduction through the walls of the axle housing heat the exterior surface of the axle housing and provide increased surface area for heat to be convected away by ambient air.
In some instances, however, convection to and from the axle housing surfaces is insufficient to remove braking heat rapidly enough, and the axle lubricant consequently becomes excessively hot (e.g., above 300 degrees Fahrenheit). This is injurious not only to the lubricant itself (accelerating oxidation and breakdown), but also to the bearings and seals associated with the axle shaft.
Typically, the brake is a wet multiple disk brake; xe2x80x9cwetxe2x80x9d, because the disks rotate through a bath of lubricating oil. As the multiple brake disks rotate through the lubricating oil, braking heat is transferred from the disks to the lubricating oil.
The temperature of the lubricating oil consequently increases, and some of the heat within the lubricating oil is transferred to the axle shaft and to the axle housing. The axle shaft and axle housing are of limited size and mass and, hence, of limited heat capacity. Therefore, their temperatures begin to approach (under the duty cycle of frequent stops characteristic of a loader) the temperature of the lubricating oil because ambient air typically does not convect heat from the axle housing as rapidly as the brake convects heat into the lubricating oil. It is therefore necessary to actively cool the lubricating oil.
While one can add a cooling loop to an axle assembly and pump hot lubricating oil through a fan-cooled radiator, this is a costly and cumbersome approach. Further, it increases the number of opportunities for leakage or contamination of the lubricating oil in what is typically a dirty and dusty environment.
It would be advantageous to provide an apparatus and method of removing excessive heat from the axle lubricant, thereby cooling the axle assembly, without substantially increasing the risks of lubricant leakage and/or contamination.
One embodiment of the invention relates to a work vehicle including a frame and an axle assembly coupled to the frame. The axle assembly includes an axle shaft and an axle housing. The axle shaft is disposed substantially within the axle housing, and a wheel is coupled to the axle assembly. An axle lubricating fluid is disposed within the axle housing. An axle cooling device is also disposed within the axle housing, in contact with at least a portion of the lubricating fluid, and is configured as a coil including a plurality of elongate tubes.
Another embodiment of the invention relates to an axle assembly for a work vehicle. The axle assembly includes a first axle shaft and a first axle housing, and a second axle shaft and a second axle housing. The first and second axle shafts are disposed substantially within the first axle housing and the second axle housing, respectively. The second axle shaft and the second axle housing are disposed coaxial with, and in opposing relationship to, the first axle shaft and the first axle housing, respectively. This embodiment further includes a first cooling device disposed within the first axle housing, and a second cooling device disposed within the second axle housing. It further includes a differential gearset housing positioned intermediate the first and second axle housings and defining a chamber configured to receive a differential gearset. A differential gearset may also be included, and is disposed within the chamber and is rotatively coupled to the first and second axle shafts. Further included are a lubricating fluid disposed within the first and second axle housings. Still further included are a first axle cooling device including a first plurality of elongate tubes and disposed within the first axle housing, and a second axle cooling device including a second plurality of elongate tubes and disposed within the second axle housing.
Another embodiment of the invention relates to a method of cooling an axle assembly of a work vehicle. The axle assembly includes an axle shaft, an axle housing configured to substantially surround the axle shaft, a cooling coil housed within the axle housing and having a passage therethrough and outer and inner surfaces, a lubricating fluid disposed within the axle housing, and a cooling fluid disposed within the passage. The lubricating fluid is of a higher temperature than is the outer surface of the coil, and the outer surface of the coil is of a higher temperature than is the cooling fluid. The method includes a step of removing heat from the lubricating fluid by placing the lubricating fluid in contact with the outer surface of the coil. The method also includes a step of removing the heat from the inner surface of the coil by circulating the cooling fluid through the passage.